JP5759337B2 - Position control device - Google Patents

Description

  The present invention relates to a position control device for a feed shaft (table) in a machine tool or the like.

  Various attempts have been made to operate a feed axis of a machine tool at high acceleration / deceleration and suppress mechanical vibration. In order to suppress mechanical vibration during acceleration / deceleration, a moving average process and filter are added to the position command to reduce the command component corresponding to the natural vibration frequency of the feed shaft, thereby eliminating the excitation force during acceleration / deceleration. it can. As a result, it is possible to control the feed shaft while suppressing mechanical vibration. However, the natural vibration frequency of the feed shaft mechanism is due to wear of drive system parts due to secular change, loose parts, decrease in ball screw tension due to temperature increase during continuous operation, change in machine installation status (balance), etc. Changes, the position averaging process and the filter become unmatched, and there is a problem that mechanical vibration occurs.

  FIG. 5 shows a control block diagram of the prior art for suppressing mechanical vibration. The value output from the position command calculator 1 is subjected to the N1 stage moving average process by the moving averager 2, the N2 stage moving average process by the moving averager 3, and the filter process by the position command filter 18. Pc is calculated. By performing the moving average process, the controlled object is gradually accelerated at the beginning of movement, becomes a constant acceleration, and further gradually decelerates before stopping. Such a position command is called an S-shaped position command because the position command value draws an S-shape. The position detection value Pm of the position detector 11 attached to the motor 12 is used as a feedback value to calculate the control error of the position command Pc, that is, the position deviation Pdif (subtracter 4). Then, the speed command calculation unit 5 multiplies the proportional gain Kp based on the position deviation and outputs a speed command Vc. The differentiator 15 differentiates the position detection value Pm and outputs a motor speed detection value Vm. The difference between the speed command Vc and the detected speed value Vm of the motor is obtained by a subtractor 6 to obtain a speed control error, that is, a speed deviation, and this is output. Based on this speed deviation, speed loop proportional gain Pv, and speed loop integral gain Iv, speed deviation proportional calculator 7 and speed deviation integral calculator 8 output a speed deviation proportional component and a speed deviation integral component, respectively, and adder 9 The deviation proportional component and the speed deviation integral component are added to output a torque command Tc. Symbol 10 in FIG. 5 indicates various filter units and current control units for filtering the torque command. A feed shaft (table) 13 is driven via a ball screw 14 to control its position.

The transfer function F (s) of the position command filter 18 is represented by (Equation 1). In (Expression 1), s represents a Laplace operator.
F (s) = (s ² + ω ₂ ² ) / (s ² + 2ζ ₂ ω ₂ + ω ₂ ² ) (Equation 1)
Where ζ ₂ : filter attenuation ratio
ω ₂ : natural angular frequency of the filter
ζ ₂ , ω ₂ > 0

The position command filter 18 calculates a position command that does not include the frequency component of ω ₂ . Moreover, if substantially equal to the natural angular frequency is omega ₀ of the feed axis _{ω 2 (ω 2 ≒ ω 0} ), the natural angular frequency of the feed shaft that is included in the position command Pc is reduced. As a result, the excitation force of the natural angular frequency of the feed shaft is reduced, and mechanical vibration of the feed shaft can be suppressed. A position control device that performs an S-shaped position command is described in Patent Document 1 below.

JP 2004-272749 A

  In the prior art shown in FIG. 5, when the rigidity of the feed shaft drive system is reduced due to machine aging, or when a heavy workpiece more than expected is placed on the table in a large machining center or the like, the feed shaft resonance frequency is lowered. Low frequency vibration occurred. In addition, the balance of machine installation was lost, the natural vibration frequency of the entire machine different from the feed shaft drive system changed, and low frequency vibration occurred during acceleration / deceleration. Furthermore, even when a mechanical failure occurs and the rigidity of the feed shaft drive system is reduced, the machine may be operated without being noticed, and the feed shaft mechanism parts such as tack bearings may be damaged by low frequency vibration.

  A position control device according to the present invention generates an S-shaped position command by performing a moving average process on a position command, and controls a feed shaft or a feed shaft as a control target in a position control device that performs position control of the feed shaft. The number of stages of the moving average in the moving average process is changed according to the magnitude of the vibration of the system including. The moving average stage number refers to the number of samples in one calculation of the average value. Since samples are acquired at each sampling period, the number of samples matches the number of sampling periods within the sampling period for calculating the moving average.

  When the vibration of the controlled object increases, the number of moving average steps can be increased.

  A position control device according to the present invention includes a position command calculating unit that generates a position command, a moving average unit that generates an S-shaped position command by performing a moving average process on the generated position command, and an S-shaped position command. A motor driving unit that controls the motor based on the position, a position detecting unit that detects the rotational position of the motor, an error calculating unit that calculates a position control error from the S-position command and the rotational position of the motor, and a position control error And a moving average stage number changing unit that changes the number of moving average stages in the moving average process based on the amplitude of fluctuation.

  The motor drive unit can perform feedback control based on the S-position control command. In the feedback control, the rotational position of the motor, that is, the rotational position of the rotor with respect to the stator of the motor may be detected to provide feedback for the position command. Further, when the speed command is generated based on the position command, the detected rotational position of the motor may be differentiated, and this differential value may be fed back to the speed command.

  The fluctuation amplitude of the position control error can be monitored in a predetermined frequency range, and the number of moving average stages can be increased when the magnitude of the vibration component in this range becomes larger than a predetermined value. .

  The number of stages of the moving average can be gradually increased, and can be increased until the vibration to be controlled becomes equal to or less than the predetermined value. When the number of stages continues to increase and reaches another predetermined value, this can be notified.

  Another position control device according to the present invention is a position control device that controls a feed position of a feed shaft by a motor, and a position command calculation unit that generates a position command and a moving average process for the generated position command. A moving average unit for generating an S-shaped position command, a speed command calculating unit for generating a speed command based on the S-shaped command, a torque command calculating unit for generating a torque command based on the speed command, a torque command And a moving average stage number changing unit that changes the number of moving average stages in the moving average process based on the amplitude of fluctuation.

  The speed command calculation unit may perform feedback control based on the S-shaped position command. In addition, the torque command calculation unit may perform feedback control based on the speed command.

  The amplitude of fluctuation of the torque command is monitored in a predetermined frequency range, and when the magnitude of the vibration component in this range becomes larger than a predetermined value, the moving average stage number can be increased.

  The number of stages of the moving average can be gradually increased, and can be increased until the vibration to be controlled becomes equal to or less than the predetermined value. When the number of stages continues to increase and reaches another predetermined value, this can be notified.

According to the position control device of the present invention, when the rigidity of the feed shaft drive system is reduced, the natural vibration frequency is changed, and vibration is generated, the number of moving average stages for generating the S-shaped position command is changed. As a result, the natural vibration frequency of the feed shaft included in the position command Pc is reduced, the excitation force is reduced, and vibration can be suppressed.

  Furthermore, when the number of moving average stages becomes large, the state is notified so that the machine is not seriously damaged.

It is a block diagram which shows embodiment of this invention. It is a block diagram which shows other embodiment of this invention. It is a block diagram which shows the structural example of the moving average stage number change device of this invention. It is a block diagram which shows the other structural example of the moving average stage number change device of this invention. It is a block diagram which shows a prior art. It is effect explanatory drawing of this invention.

  An embodiment of the present invention will be described. The same elements as those of the conventional example are denoted by the same reference numerals, and description thereof is omitted. A control block diagram of this embodiment is shown in FIGS.

  The value output from the position command calculator 1 is subjected to N1 stage moving average processing by the moving averager 2 and N2 stage moving average processing by the moving averager 3 to calculate the position command Pc. The position detection value Pm of the position detector 11 attached to the motor 12 is used as a feedback value to calculate the control error of the position command Pc, that is, the position deviation Pdif (subtracter 4). Then, the speed command calculation unit 5 multiplies the proportional gain Kp based on the position deviation and outputs a speed command Vc. The differentiator 15 differentiates the position detection value Pm and outputs a motor speed detection value Vm. The difference between the speed command Vc and the detected speed value Vm of the motor is obtained by a subtractor 6 to obtain a speed control error, that is, a speed deviation, and this is output. Based on this speed deviation, speed loop proportional gain Pv, and speed loop integral gain Iv, speed deviation proportional calculator 7 and speed deviation integral calculator 8 output a speed deviation proportional component and a speed deviation integral component, respectively, and adder 9 The deviation proportional component and the speed deviation integral component are added to output a torque command Tc. A symbol 10 in FIG. 1 indicates various filter units and a current control unit that filter the torque command. The feed shaft (table) 13 is driven through the ball screw 14 obtained by the moving average process, and its position is controlled. A motor drive unit having a configuration indicated by reference numerals 4 to 11 drives and controls the motor 12 based on the S-shaped position command obtained by the moving average process.

  The moving average stage number changer 16 changes the moving average stage number N2 of the moving averager 3 from the position deviation Pdif. Alternatively, the moving average stage number changer 16 changes the moving average stage number N2 of the moving averager 3 based on the torque command Tc.

  A specific configuration example of the moving average stage number changer 16 is shown in FIG. An FFT (Fast Fourier Transform) calculator 161 calculates the spectrum maximum value SPm of the vibration component from the position deviation Pdif or the torque command Tc by a known method. The frequency range for monitoring the spectrum can be determined in advance. In this configuration example, monitoring is performed in the range from fst to fen. The comparator 163 outputs a pulse to the full adder 165 when the spectrum maximum value SPm exceeds a preset comparison value SPref162. The full adder has an initial value N2, and outputs N2 'increased by ΔN2 by the pulse to the moving averager 3. The moving averager 3 performs moving average processing by changing the number of moving average stages from N2 to N2 '.

  The moving average stage number changer 16 compares the vibration component by a full adder when the fluctuation of the position deviation Pdif or the torque command Tc becomes large, particularly when the vibration component included in the position deviation or the torque command becomes large. ΔN2 is added to the moving average number of stages until the value SPref is less than or equal to the value SPref, and sequentially increased. In FIG. 6, the gain frequency characteristics of the position command Pc with N1 = 100 and N2 = 20 in the sampling period 1 ms are indicated by dotted lines, and the gain frequency characteristics of N1 = 100 and N2 = 40 are indicated by solid lines. In the system having the characteristic indicated by the dotted line in FIG. 6, when the natural frequency of the control object changes from 30 Hz to 25 Hz due to secular change or the like, the gain at the natural frequency increases as indicated by the arrow. For this reason, the natural vibration frequency component included in the position command Pc increases and the excitation force increases, so that mechanical vibration occurs. When vibration occurs, full adder 165 increases the moving average stage number until the vibration component becomes smaller than preset comparison value SPref. For example, when N2 increases to 40, as can be seen from FIG. 6, the natural vibration frequency component (30 Hz) included in the position command Pc is reduced, the excitation force is reduced, and vibration can be suppressed.

Another configuration example of the moving average stage number changing unit 16 is shown in a block diagram in FIG. When the vibration component at a frequency in a preset range exceeds a preset spectrum comparison value SPref by a known FFT or the like from the position deviation Pdif or the torque command Tc, the FFT processor 161 detects the vibration. The frequency fp of the component is calculated. The divider 172 outputs the moving average stage number N2 ′ to the moving averager 3 from (Equation 2). In (Expression 2), Ts indicates a sampling period.
N2 ′ = 1 / (fp × Ts) (Formula 2)
The moving averager 3 performs moving average processing by changing the number of moving average stages from N2 to N2 ′.

  When the vibration component included in the position deviation Pdif or the torque command Tc increases, the moving average stage number changing unit 16 detects the vibration frequency fp by the FFT calculator 161, and a new moving average stage number is obtained from (Equation 2). N2 ′ is calculated. For example, when the natural vibration frequency changes to 25 Hz and the sampling period is 1 ms, the moving average stage number changer outputs N2 ′ = 40 from (Equation 2). FIG. 6 shows the gain frequency characteristics of the position command Pc with N1 = 100 and N2 = 40 in a sampling cycle of 1 ms by a solid line. The vibration frequency near 25 Hz included in the position command Pc is reduced, and the excitation force is reduced. It becomes smaller and vibration can be suppressed.

  As shown in FIG. 3 and FIG. 4, the moving average stage number changing unit 16 can have a function of warning when vibration becomes large. The comparator 167 detects that the state of the machine is abnormal when the moving average stage number N2 ′ exceeds a preset threshold value N2ref, and the notification unit 168 displays the state and notifies by voice or the like. To do. When the vibration is generated because the rigidity is lowered, the moving average stage number N2 'is increased, so that a warning or the like can be transmitted to the operator or the like. In response to this warning, the operator can stop the corresponding axis, and if there is a mechanical failure, the operator will not be unaware of it and the feed shaft mechanism will be damaged. Disappear.

  1 position command calculator, 4, 6 subtractor, 2, 3 moving averager, 5 speed command calculator, 7 speed deviation proportional calculator, 8 speed deviation integral calculator, 9 adder, 10 various filter units, current control , 11 Motor position detector, 12 Motor, 13 Table, 14 Ball screw, 15 Differentiator, 16 Moving average stage number changer, 161 FFT calculator, 162, 164, 166, 169, 171 Coefficient, 163, 167 Comparator, 165 full adder, 170 multiplier, 172 divider, 18 position command filter.

Claims (3)

A position control device for controlling a feed position of a feed shaft by a motor,
A position command calculation unit for generating a position command;
A moving average unit that generates an S-shaped position command by performing a moving average process on the generated position command;
A motor drive unit for driving and controlling the motor based on the S-position command;
A position detector for detecting the rotational position of the motor;
An error calculator that calculates a position control error from the S-position command and the rotational position of the motor;
Based on the amplitude of the fluctuation of the position control error, a moving average step number changing unit that changes the number of moving average steps in the moving average process,
A position control device. A position control device for controlling a feed position of a feed shaft by a motor,
A position command calculation unit for generating a position command;
A moving average unit that generates an S-shaped position command by performing a moving average process on the generated position command;
A speed command calculation unit that generates a speed command based on the S-position command;
A torque command calculation unit that generates a torque command based on the speed command;
Based on the amplitude of fluctuation of the torque command, a moving average step number changing unit that changes the number of moving average steps in the moving average process;
A position control device. The moving average step number changing unit gradually changes the moving average step number,
The position control device according to claim 1, further comprising a notifying unit that notifies when the number of stages of the moving averager is larger than a preset threshold value.

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